Aqueous dispersions comprising polyurethane and ethylenic copolymers for heat sealable coatings
A film forming aqueous dispersion having utility as heat seal coatings for blister packaging applications comprises a blend of 10-90% by weight of one or more polyurethane dispersions; 90-10% by weight one or more compatible ethylenic copolymer dispersions/emulsions; an anti-blocking additive at 0.1-12 weight % of the total solids; and optional additives including wetting, defoaming, thickener, antifungal additives. The heat seal coating compositions provide enhanced and balanced properties such as a reduction of organic solvents, a tack free coating surface off the press, good press runnability, easy clean-up, antiblocking from ambient temperature to 50° C., heat-activation with no pot life at elevated temperatures, and, heat sealability to various plastic substrates including Virgin Poly(ethylene terephthalate) (PET), recycle PET (RPET), Amorphous PET (APET), PET-Glycol modified (PETG), PETG/APET/PETG (GAG) and Polyvinyl chloride (PVC).
1. A film forming aqueous dispersion coating composition having utility as a heat seal coating for blister packaging applications comprising:
A) 10% to 90% by weight of one or more polyurethane dispersions having a melting point when dried in the range of −30° C. to 120° C.;
B) 90% to 10% by weight of one or more compatible ethylenic copolymer dispersions;
C) an anti-blocking additive at 0.1-12 weight % of total solids; and
D) optionally one or more wetting, defoaming, thickener, or antifungal additives;
the heat seal coating when dried having a shear storage modulus G′ at a heat seal activation temperature range of 170° F.-240° F. in the range of 3.5×10 4 to 6.0×10 5 Pascals; the ethylenic copolymer dispersion having a glass transition temperature Tg in the range of −30° C. to 130° C.
2. The film forming aqueous dispersion coating composition of claim 1 wherein a solid resin weight ratio between A and B is in a range of 15/85 to 85/15.
3. The film forming aqueous dispersion coating composition of claim 1 , wherein the ethylenic copolymer dispersion comprises a styrene monomer content of less than 80% by weight.
4. The film forming aqueous dispersion coating composition of claim 1 , wherein the anti-blocking additive is selected from waxes or inorganic particles.
5. The film forming aqueous dispersion coating composition of claim 4 wherein the wax is in a micronized form or is an aqueous paste and has a melting point higher than 60° C. and is present in a range of 0.1 to 12 weight % of total solids.
6. The film forming aqueous dispersion coating composition of claim 1 , wherein the one or more polyurethane dispersions has a melting point or softening point in the range of −25° C. to 110° C.
7. The film forming aqueous dispersion coating composition of claim 6 , wherein the one or more polyurethane dispersions has a melting point of −15° C. to 100° C.
8. The film forming aqueous dispersion coating composition of claim 1 , wherein the ethylenic copolymer dispersion has a glass transition temperature, Tg, in the range of −20° C. to 120° C.
9. The film forming aqueous dispersion coating composition of claim 1 , wherein the ethylenic copolymer dispersion has a glass transition temperature, Tg, in the range of −10° C. to 110° C.
10. The film forming aqueous dispersion coating composition of claim 3 , wherein the styrene monomer content in the copolymer is less than 50% by weight.